Method of storing heavy hydrocarbon materials in subterranean facilities

ABSTRACT

A method of storing high-viscosity, non-pumpable, hydrocarbon materials in subterranean storage facilities is provided. The method comprises the sequential steps of purging the storage facilities with a carbon dioxide-containing fluid to provide a carbon dioxide atmosphere therein, admixing an effective amount of carbon dioxide with the hydrocarbon material to sufficiently lower the viscosity of the hydrocarbon material, injecting the carbon dioxide-containing hydrocarbon material into the storage facilities, and maintaining a carbon dioxide atmosphere in the facilities while same contains the carbon dioxide-containing hydrocarbon.

United States Patent Shock et al. 1 1 Dec. 2, 1975 l l METHOD OF STORING HEAVY 3,804,752 4/1974 Merrill, Jr. ct al l37/l3 X HYDROCARBON MATERIALS IN SUBTERR N N FACILITIES Primary Examiner.lacob Shapiro A A t, F F. [75] Inventors: DArcy A. Shock; Fred J. Raid, nomey gen or Lindsey Scott both of Ponca City, Okla. ABSTRACT [73] Asslgnee: Cfmtmemal Culpany ,Ponca A method of storing high-viscosity, non-pumpable, hy-

Okla drocarbon materials in subterranean storage facilities [22] Fil d; F b, 18, 1975 is provided. The method comprises the sequential steps of purging the storage facilities with a carbon [2]] Appl' 550891 dioxide-containing fluid to provide a carbon dioxide atmosphere therein, admixing an effective amount of 52] us. Cl 61/.5; 137/13 carbon dioxide with the hydrocarbon material to 51 1111.01. B650 5/00; F17D 1/16 oiontly lower the viscosity of the hydrocarbon moto- [58] Field of Search 61/.5; 137/13 rial. injecting the carbon dioxido-oontaining hydrocarbon material into the storage facilities, and maintain- 5 Refer Cited ing a carbon dioxide atmosphere in the facilities while UNITED STATES PATENTS same contains the carbon dioxide-containing hydro- 3,438,203 4/1969 Lamb ct al 6l/.5 carbon. 3,618,624 11/1971 Vairogs 137/13 5 Claims, N0 Drawings METHOD OF STORING HEAVY HYDROCARBON MATERIALS IN SUBTERRANEAN FACILITIES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the storage of high-viscosity, non-pumpable hydrocarbon materials. In one aspect it relates to a method of storing, in subterranean storage facilities, a hydrocarbon material having a viscosity sufficiently high to resist free-flow.

2. Brief Statement of the Prior Art In recent years the amount of crude oil and hydrocarbon products required for US. consumption has substantially increased. The amount of crude oil and other hydrocarbon products produced in the US. has not been sufficient to meet this increased demand. Therefore, it has become necessary to import crude oil and other hydrocarbon products. With the need for imported crude, it is becoming necessary to store large quantities of such heavy crude. The most ecologically acceptable and inexpensive storage known is in solution cavities and excavated underground caverns. The use of such mined underground caverns has been successfully employed for storage of light hydrocarbon materials. However, much of the imported crude is of high viscosity and low pour point and thus cannot be readily stored underground, even though, from a safety and/or operational reason, such underground storage of the heavy crude is preferred. Thus, new methods for storing and improving the flow characteristics of heavy crude oils are constantly being sought.

OBJECTS OF THE INVENTION An object of the present invention is to provide a method of storing high-viscosity, non-pumpable hydrocarbon materials.

Another object of the invention is to provide a method of storing heavy crude oil in subterranean storage facilities.

Another object of the invention is to provide a method of storing high-viscosity, non-pumpable hydro-.

carbon in subterranean formations wherein the stored hydrocarbon can readily be recovered.

These and other objects, advantages, and features of the present invention will be apparent to those skilled in the art from a reading of the following detailed description.

SUMMARY OF THE INVENTION According to the present invention, we have found a method of storing heavy crude in subterranean storage facilities. More specifically, we have found a method for storing, in subterranean storage facilities, a crude having a viscosity sufficiently high to resist free-flow which comprises the sequential stepsof purging the storage facilities with a carbon dioxide containing fluid DESCRIPTION OF THE PREFERRED EMBODIMENTS The problem of storage of heavy crude and other heavy hydrocarbon materials has long been recognized by the oil industry. The problem has become even more acute due to the large quantities of oil imported. The term heavy crude and/0r heavy hydrocarbon materials as used herein is to be understood to mean petroleum crude oil and hydrocarbon materials which have a viscosity sufficiently high to resist a free-flow. Generally, a crude or hydrocarbon material having a viscosity of 2,500 centipoises or higher in non-pumpable and thus considered to be resistant to free-flow. However, from a practical standpoint, it is desirable that the crude and- /or hydrocarbon material have a viscosity of less than 600 centipoises so that same is easily pumpable.

We have now found a method for storing heavy crude oil and/or hydrocarbon materials in subterranean storage facilities which involves reducing the viscosity of the substance to be stored so that same is easily pumpable and maintaining the substance at a reduced viscosity throughout the storage period. Such can be readily accomplished by employing the sequential steps of:

a. purging the proposed storage facilities with a carbon dioxide containing fluid to provide a carbon dioxide atmosphere therein;

b1 admixing an effective amount of carbon dioxide with the heavy crude oil and/or hydrocarbon material to saturate same;

c. injecting the carbon dioxide saturated crude and- /or hydrocarbon material into the storage facility; and

d. maintaining a carbon dioxide atmosphere within the storage facility while crude and/or hydrocarbon material is contained therein.

Any suitable underground storage facility capable of receiving the crude or hydrocarbon material without creating problems in recovery of such crude or-hydrocarbon material can be employed. Examples of suitable storage facilities include solution mined cavities; mined underground caverns; reconverted underground mineral mines, such as iron mines; and the like. It is, of course, necessary that the facility not contain fractures and the like through which the stored product could be lost. Also, since it is desirable to maintain a carbon dioxide atmosphere within the facility, fractures or formations of high permeability and porosity, such as coal mines, would be unsuitable. Solution-mixed cavities in salt domes, mineral underground caverns, and reconverted mineral mines are especially suited for use as storage facilities when employing the method of the present invention.

Once a solution-mined cavity or a reconverted mine has been determined to be suitable as a storage facility, the facility is equipped with the necessary equipment, such as well bores, compressors,'pumps, pressure control means, and the like. While it is evident that such equipment is necessary to allow one to purge the facility with a carbon dioxide-containing fluid, to inject the mixture of CO and the heavy crude or hydrocarbon material, to maintain a carbon dioxide-enriched atmosphere at the desired pressure in the storage facility, and to recover the material from the facility, such equipment is well known in the oil industry, and, as such, is not considered a part of the present invention. The storage facility is then purged with a carbon dioxide-containing fluid for a sufficient period of time to insure that the facility is provided with a carbon dioxideenriched atmosphere. The carbon dioxide-containing fluid employed as the purging agent can be gaseous carbon dioxide or a gas containing at least 20 weight percent, preferably-at least about 50 weight percent carbon dioxide. Flue gas materials and other carbon dioxide-containing materials may be used, provided that the ultimate carbon dioxide pressures are reached.

The heavy crude and/or hydrocarbon material to be stored in the facility is then admixed with an effective amount of gaseous carbon dioxide to reduce the viscosity of the product so that same can readily be injected into the storage facility. Generally, the carbon dioxide is admixed with the heavy crude and/or hydrocarbon material under pressure to ensure complete dispersement of the carbon dioxide in the heavy product. While the pressure at which the carbon dioxide is maintained during the mixing procedure can vary widely, it is generally desirable that the carbon dioxide be maintained at a pressure from about 800 to 1,000 psi and that suffi- -cient carbon dioxide be employed to saturate the crude or hydrocarbon material. By admixing carbon dioxide with a heavy petroleum product, the viscosity of the product is substantially reduced. The use of carbon dioxide to reduce the viscosity of a crude oil or hydrocarbon material has been found to be much more effective on heavy crude oil or hydrocarbon than on light oils and hydrocarbons.

The carbon dioxide-containing crude and/or hydrocarbon material is then injected by conventional means, such as pumps, into the subterranean storage faciliity. Since the storage facility has been previously purged with a carbon dioxide-containing fluid, the crude and/or hydrocarbon material is injected into the storage facility under sufficient pressure to overcome the pressure within the facility. The gaseous product displaced by the injected crude and/or hydrocarbon material can be readily collected at the surface for use in subsequent purging or product recovery operations. When carbon dioxide is used as the purging agent, it can be collected, compressed, and admixed with additional heavy crude and/or hydrocarbon material in order to reduce the viscosity of same.

Once the cavity is filled with the product being stored or all of the incoming product has been injected into the storage facility, a carbon dioxide atmosphere is maintained in the facility to insure complete dispersement and solution of carbon dioxide throughout the stored product so that the reduced viscosity of the product can readily be maintained. When the product is stored for long periods of time, additional carbon dioxide may be required to be dispersed in the storage facility to maintain the desired atmosphere therein.

The stored petroleum products can readily be removed from the storage facility by any suitable: means such as by pressuring the facility on the upper portion with a carbon dioxide-containing gas or by bottom-hole pumps. Once the crude oil and/or hydrocarbon has been recovered, the carbon dioxide contained therein can be recovered for subsequent use. For instance, the

carbon dioxide can be recovered by decreasing the pressure on the stored product as it leaves the storage facility, thus allowing the carbon dioxide to be flashed out and collected. The collected carbon dioxide can then be used to purge the storage facility, to recover the stored product, or to be admixed with additional heavy crude and/or hydrocarbon material to reduce the viscosity of same.

When additional petroleum products are not being stored in the facility, the recovered carbon dioxide can readily be stored in the subterranean storage facility.

While the present invention has been described with reference to heavy crude and/or heavy hydrocarbon materials, it is to be understood that the method of reducing the viscosity of such products and the storage of same is applicable to any crude and/or hydrocarbon material in which storage of same can be simplified using the method of the present invention.

Having thus described the invention, we claim:

1. A-method of storing in subterranean storage facilities a hydrocarbon material having a viscosity sufficiently high to resist free-flow which comprises:

a. purging said storage facilities with a fluid comprising carbon dioxide to provide a carbon dioxide atmosphere;

b. admixing an effective amount of carbon dioxide with said hydrocarbon material to saturate same and reduce the viscosity of same to below 2500 centipoise.

c. injecting said carbon dioxide-saturated hydrocarbon material into said storage facilities; and,

d. maintaining said carbon dioxide atmosphere in said facilities while same contains said carbon dioxide-saturated hydrocarbon material.

2. The method of claim 1 wherein said carbon dioxid; is maintained at a pressure of from about 800 to 1,000 psi during the mixing of same with said hydrocarbon material and the injection of such carbon dioxidesat'urated hydrocarbon material into said storage facilities.

3. The method of claim 2 which includes the step of recovering said carbon dioxide-saturated hydrocarbon material from said storage facilities and separating said CO from said hydrocarbon material.

4. The method of claim 3 wherein said carbon dioxide-saturated hydrocarbon is recovered by injecting into said storage facilities under sufficient pressures, a gas comprising carbon dioxide and wherein said carbon dioxide is recovered from said hydrocarbon material when same has been transferred from said storage facilities by decreasing the pressure on said saturated hydrocarbon material.

5. The method of claim 4 wherein said CO recovered is recycled to said facilities. 

1. A METHOD OF STORING IN SUBSTERRANEAN STORAGE FACILITIES A HYDROCARBON MATERIAL HAVING A VISOSITY SUFFICIENTLY HIGH TO RESIST FREE-FLOW WHICH COMPRISES: A. PURGING SAID STORAGE FACILITIES WITH A FLUID COMPRISING CARBON DIOXIDE TO PROVIDE A CARBON DIOXIDE ATMOSPHERE; B. ADMIXING AN EFFECTIVE AMOUNT OF CARBON DIOXIDE WITH SAID HYDROCARBON MATERIAL TO SATURATE SAMEL AND REDUCE THE VISCOSITY OF SAME TO BELOW 250 CENTIPOISE. C. INJECTING SAID CARBON DIOXIDE-SATURATED HYDROCARBON MATERIAL INTO SAID CARBON DIOXIDE ATMOSPHERE IN SAID FACILID. MAINTAINING SAID CARBON DIOXIDE ATMOSPHERE IN SAID FACILITIES WHILE SAME CONTAINS SAID CARBON DIOXIDE-SATURATED HYDROCARBON MATERIAL.
 2. The method of claim 1 wherein said carbon dioxide is maintained at a pressure of from about 800 to 1,000 psi during the mixing of same with said hydrocarbon material and the injection of such carbon dioxide-saturated hydrocarbon material into said storage facilities.
 3. The method of claim 2 which includes the step of recovering said carbon dioxide-saturated hydrocarbon material from said storage facilities and separating said CO2 from said hydrocarbon material.
 4. The method of claim 3 wherein said carbon dioxide-saturated hydrocarbon is recovered by injecting into said storage facilities under sufficient pressures, a gas comprising carbon dioxide and wherein said carbon dioxide is recovered from said hydrocarbon material when same has been transferred from said storage facilities by decreasing the pressure on said saturated hydrocarbon material.
 5. The method of claim 4 wherein said CO2 recovered is recycled to said facilities. 